Methods of preparing halosilanes are known in the art. Typically, halosilanes are produced commercially by the Mueller-Rochow Direct Process, which comprises passing a halide compound over zero-valent silicon (Si0) to obtain a gas-solid direct contact between the Si0 and the halide compound, resulting in the production of a mixture of halosilane compounds. The typical process for making the Si0 used in the Direct Process involves carbothermic reduction of silicon dioxide (SiO2) in an electric arc furnace. In a typical submerged arc furnace process, a mixture of carbon and SiO2 is added to the top of the furnace. Both alternating current (AC) arc furnaces and direct current (DC) power sources may be used. U.S. Pat. No. 5,009,703 and the references cited therein describe production of Si0 from SiO2. The overall reaction can be represented as follows: SiO2+2C→Si0+2CO. The Si0 produced by this process is typically at least 98% pure.
Products, which include mixtures of halogenated silicon containing compounds, are produced by the Direct Process. When an organohalide is used as the halide compound, a copper catalyst and various optional promoters are added to the Si0, and the product includes a mixture of organohalosilanes (organic Direct Process). When a hydrogen halide is used as the halide compound, the product includes a mixture of inorganic hydrogen-functional halosilanes (inorganic Direct Process). Typically, catalyst and promoters are not added to the Si0 in the inorganic Direct Process.
Frequently, the inorganic Direct Process has been run in a continuous or semi-batch mode. During a production campaign, the inorganic Direct Process is initiated by charging a reactor with a contact mass comprising fresh silicon that is free of catalyst and promoters, e.g., Si0 prepared by carbothermic reduction as described above. A hydrogen halide and additional fresh silicon are added to the reactor to produce the product. When selectivity toward monohydrogentrihalosilane in the product drops to an undesirable level, the production campaign is ended by shutting down the reactor and discarding any silicon remaining therein.